Researchers from the University of New South Wales in Australia and Purdue University in the US said global warming will not stop after 2100, the point where most previous projections have ended.

In fact temperatures may rise by up to 12C (21.6F) within just three centuries making many countries into deserts. The study, published in the prestigious journal Proceedings of the National Academy of Sciences, said humans will not be able to adapt or survive in such conditions.

Professor Tony McMichael, one of the authors, said if the world continues to pump out greenhouse gases at the current rate it will cause catastrophic warming.

"Under realistic scenarios out to 2300, we may be faced with temperature increases of 12 degrees or even more," he said. "If this happens, our current worries about sea level rise, occasional heatwaves and bushfires, biodiversity loss and agricultural difficulties will pale into insignificance beside a major threat - as much as half the currently inhabited globe may simply become too hot for people to live there."